IP-based telecommunications enable multimedia communications (e.g. voice, video, etc.) over IP networks. For example, the IP Multimedia Subsystem (IMS) is the technology defined by the Third Generation Partnership Project (3GPP) to provide IP Multimedia services over (mobile) communication networks. The IMS is described further below in relation to FIG. 1, which illustrates schematically how the IMS fits into the mobile network architecture in the case of a General Packet Radio Service (GPRS) access network.
A problem arises when information media (e.g. voice/audio or video) such as an announcement needs to be played to either the calling or the called party, especially when one party or both parties are connected to a visited IP network rather than to the home IP network (e.g. is located in a foreign country). In such cases the media is typically routed from a server or other entity in the subscriber's home network where the media is stored to the terminal of the served subscriber (calling or called party). This may involve routing the media over a large distance. A particular example of this problem is described below for the case of Voice over LTE (VoLTE) communications, but the problem and solutions described are not limited to such communications.
The 3GPP has also developed the System Architecture Evolution (SAE) as the evolved core network architecture, and Long Term Evolution (LTE) wireless mobile telecommunications standard as the evolved mobile radio access network. The SAE architecture is entirely IP-based, with separation of control plane and user plane. The main component of the SAE architecture is the Enhanced Packet Core (EPC). The EPC serves as the equivalent of a GPRS network. The LTE standard only supports packet switching (PS), whereas in many legacy networks voice (and other media) calls are circuit switched (CS). The adoption of LTE means that carriers have to re-engineer their voice call network, and the preferred approach is to use VoLTE (Voice over LTE), which is based on the IMS.
In IP networks in general, and particularly in the context of VoLTE, great effort is taken to optimize the media stream (user plane) for person-to-person communications. Specifically, when a voice or video call is established between a calling party that is roaming in one country to a called party in another country, the user plane (as well as the control plane) is carried directly from the country in which the calling party currently resides to the destination country, where the called party is a subscriber. The user plane and control plane traverse the IMS interconnect network (IPX).
When an announcement (or other media) needs to be played to either the calling or the called party, the media is typically routed from a Media Resource Function (MRF) in the home IMS network towards the terminal of the served subscriber (calling or called party). In the context of the present discussion an MRF encompasses both a Media Resource Function Controller (MRFC) and a Media Resource Function Processor (MRFP). There are several ways that MRFs may be deployed, such as:
1) deploying geographically distributed MRFs—for example one IMS operator may deploy an MRF in each region, e.g. Europe, North America, Asia etc.—thereby limiting the average distance between the served subscriber and the MRF.
2) deploying shared MRFs—for example, one IMS operator may allow other operators to store media files in its MRF, and the other IMS operators may then connect their served subscribers to the shared MRF.
One disadvantage of the first method is that the IMS operator has to invest in, administer and maintain a potentially large number of MRFs spread around the globe. Furthermore, even though the average distance between served user and MRF will be reduced, the resulting effective distance may still be too large to justify the playing of announcements to roaming subscribers. Moreover, the availability of a ‘local MRF’ may differ depending on the country where the served subscriber is currently roaming. As a result, the Multi Media Telephony (MMTel) service logic that controls the communication session has to adapt its logic processing depending on the country where the subscriber is currently residing.
A disadvantage of the second method is that administrative agreements have to be made between the respective IMS operators. Also, the availability of shared MRF media files may differ from country to country. This has the effect that the MMTel service logic has to adapt its logic processing for each country. In addition, the service for the subscriber will differ for each country.
Document EP2408164 describes a system, method and service server that can exert unified media control over various kinds of media playing services and is able to play different media resources.
Document US 2006/0291638 discloses a ringback/ringtone synchronisation system for utilizing ringtones as replacement ringback announcements.